Surface tension measurement in a pressurized environment

ABSTRACT

Method and apparatus for measuring the surface tension of a liquid inside a vessel (2), reactor, or inside a section of flow-through process pipe that is pressurized above normal ambient pressure, up to but not limited, to 100 psig (7000 kPa), includes a pair of tubes (2,3) having a small and large orifice in a modular probe assembly that allows the probes to be positioned at selected and variable distances below the surface of the liquid. A high pressure source (4) provides an inert nitrogen or process gas through a pressure regulator (5) to the input of two or three mechanical or electronic mass flow controllers (6,7,8), powered by an external power supply (9), which control the bubble rate at each orifice through manual adjustments, or electronic set points determined by a computer software program, independent of the pressure in the vessel, reactor, or flow-through process pipe. One or more differential pressure transducers (10,11) measure the pressure of bubbles being formed and released from the two orifices. A transducer demodulator circuit (12) converts the resulting fluctuating pressure signal directly to an equivalent fluctuating electrical DC voltage signal. This signal is input to a (13) computer using one or more plug-in analog input/output computer interface circuit boards (14). A software program tracks the differential waveform and captures the maximum differential bubble pressure which is directly proportional to fluid surface tension. A temperature probe (15) and/or other commercially available probe (such as conductivity, viscosity, or density) is immersed at the same level as the orifices to measure liquid temperature, and/or other process parameters. A pneumatic damper (16) smoothes the large orifice signal in the single transducer apparatus (FIG. 1), whereas in a two transdcuer apparatus the average maximum values of the two individual, undampened, pressure signals are electronically substracted to provide the maximum differential bubble pressure which is directly proportional to fluid surface tension.

BACKGROUND OF THE INVENTION

The maximum differential bubble pressure method, employing two orificesof different diameters immersed in the body of a fluid was tested andproven to be adaptable for measuring in a pressurized environment overfifteen years ago as described in U.S. Pat. 4,416,148, up to a nominal10 psig pressure, at 25 degrees Celsius. Electronic hardware peakdetection for fluid surface tension measurement with the modifiedmaximum differential bubble pressure technique has proven satisfactoryfor non-viscous fluids, and fluids tested under non-pressurizedconditions. Hardware peak detection is limited to transducer outputsignals that are unipolar (positive) in value, nominally between 0 to 5,or 0 to 10 Volts DC. Hardware peak detector circuits will, however,false trigger on a zero crossing.

Electronic hardware peak detection circuits have a number of furtherlimitations when certain pneumatic conditions change the differentialpressure waveform by generating false peaks that trigger the hardwarepeak detector. Hardware peak detectors can false trigger (see FIG. 4) onpressure signal fluctuations that are caused by capillary action when0.1 mm I.D. and larger orifices are used in the small orifice position.As the viscosity of a liquid increases, there is increased hydrodynamicresistance of the liquid against a moving bubble. Very viscous fluids,and fluids with high suspended solids concentration, cause electronicpeak detectors to false trigger. Greater pneumatic pressures required toovercome the increased hydrodynamic resistance at an orifice can causeunstable or noisy waveforms.

Lowering the amplitude of the differential pressure waveform will reducethe amplitude of the false peaks proportionately so that the electronichardware peak detector no longer trigger on the false peaks; however,this can lower the amplitude of the waveform in lower surface tensionfluids to the point where they no longer trigger the electronic peakdetector. In this situation, it is no longer possible to calibrate theinstrument in a low standard calibration fluid, as for example, alcohol.

The electronic hardware peak detector will also false trigger onwaveform noise oscillations that result when the measured test fluid ispressurized. Mass flow controllers, required to operate in an increasingpressurized environment, cause a maximum bubble pressure waveform thatbecomes increasingly unstable between bubbles (FIG. 6). Largeoscillations occur following the release of each bubble before thesystem stabilizes and the next bubble is blown.

In a non-pressurized environment the bubble rate remains constant oncethe flow rate is set with mass flow controllers. However, in anincreasing pressurized environment, although the maximum bubble pressureremains constant and therefore surface tension remains constant, bubblerate will decrease (slow down) with increasing pressure (see FIGS. 4 and6).

Electronic hardware peak detection circuits are further limited inresponding to various amplitude and frequency changes of the maximumbubble pressure waveform and waveform shapes will change as bubble rateis changed, and as fluid viscosity increases. At one bubble per second,the waveform flows a sawtooth configuration (FIG. 4) where a linearpositive slope follows the increase in pressure as the bubble is formedup to its maximum bubble pressure point. When a bubble releases there isa sharp drop (negative downslope) followed by a momentary back pressureand capillary action before the pressure equalizes inside the tube andthe next bubble begins to form. The positive slope is commonly referredto as the "surface age" of the bubble while the rest is commonlyreferred to as "dead time" (FIG. 5).

An ideal hardware peak detector should track only the surface age(positive) portion of the sawtooth wave until it reaches a validmaximum, capture that maximum value, trigger a reset signal by detectingthe subsequent drop (negative downslope), and then track the next validpeak.

The dead time of a sawtooth waveform is finite and depends on therheology of the fluid, the diameter and configuration of the orifice,and the pressure characteristics of the mass flow controllers. As bubblerate increases, dead time becomes a greater proportion of thepeak-to-peak bubble interval time. At one bubble per second (FIG. 4) thesurface age typically is in excess of ninety percent of the bubbleinterval, while at thirty five or more bubbles per second, the surfaceage can be less than ten percent of the bubble interval (FIG. 5).

Mass flow controllers are set for a specific flow rate when aninstrument is set up and calibrated; however, bubble rate will change ifsurface tension of the fluid changes, even though flow rate stays fixed.A peak detector must be flexible enough to cover all possible bubbleranges. For example, a flow setting that produces one bubble per secondin water, with surface tension in the 70+dynes/cm. range, produces morethan three bubbles per second in alcohol, with surface tension typicallyin the 20 plus dynes/cm range. The waveform amplitude in alcohol is muchsmaller due to lower surface tension of alcohol. Electronic peakdetection circuits lack capability to ignore various noise oscillationsand signal combinations as described.

SUMMARY OF THE INVENTION

In the present invention, an advanced software peak detection program isprovided to solve problems encountered using hardware peak detection andto allow for accurate surface tension measurement. The resultingsoftware program used in the present invention can be extended, withminor hardware modifications, to the accurate surface tensionmeasurement of viscous fluids and fluids with high solids content inboth ambient and under pressurized conditions.

No continuous process instrument for making surface tension measurementsunder pressure is presently being marketed. There is a need for such aninstrument to measure surface tension of pressurized liquefied gases(such as natural gas, freon, and freon replacements), in latexpolymerization reactors, and in liquids and thermoplastic materials thatare produced or converted under high pressure.

It is therefore an object of this invention to provide an apparatus fordetermining surface tension of a liquid independent of the pressureenvironment of the container holding the liquid or the depth ofimmersion of the probes under the surface of the liquid.

It is another object of this invention to provide a software andhardware means to open the mass flow controller control valve to itsfull open position to increase the flow through the mass flowcontrollers to a maximum, in order to purge the probes during the periodthat a vessel, reactor, or pipe is pressurized, so as to prevent theback flow of liquid into the probes, particularly fluids with highsolids concentration that can cause plugging of the probes. This purgingcapability can also be used as a means to unplug the probes during thenormal production cycle, if needed.

It is a further object of this invention to provide a multipletransducer system so that the two sensing orifices are physicallydecoupled and the maximum bubble pressure peaks from each of the twoorifice signals are individually averaged. The maximum average of thesignal from the large orifice is electronically subtracted from themaximum average of the signal from the small orifice to provide anextremely accurate maximum differential bubble pressure value, directlyproportional to surface tension. In highly viscous fluids the ratio ofthe bubble rates can be set to make the surface tension valueindependent of viscosity effects. This is applicable in bothnon-pressurized and pressurized environments.

It is a still further objective of this invention to provide a flexible,modular, and interchangeable mechanical means for varying the immersionlength, orientation, and position of surface tension, temperature, andother similar measurement probes inside a vessel, reactor, or pipesection, both in an ambient and pressurized environment. This mechanicalmeans includes a porous basket at the end of probe which mitigates theeffect of shearing or turbulence (which would otherwise be detrimentalto the free information of bubbles at the probe orifices) from the flowor mixing of the fluid in the vessel, reactor, or pipe, while at thesame time allowing the free, non-turbulent flow of the fluid past thetension orifices and associated temperature or other measurement probes.

Other objects and advantages of the invention will be apparent from thefollowing description, the accompanying drawings and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a combined pneumatic and electrical block diagram showing thecomponents comprising the preferred embodiment of the invention using asingle differential pressure transducer and two mass flow controllers;

FIG. 2 is a combined pneumatic and electronic block diagram similar toFIG. 1 illustrating the components comprising an alternative arrangementusing two differential pressure transducers and three mass flowcontrollers;

FIG. 3 is a cross sectional view of a modular probe assembly for use inboth pressurized and non-pressurized vessels, reactors, or process pipesections, showing means for using standard and replaceable small andlarge orifice probes and other process monitoring probes such astemperature and conductivity;

FIG. 3A is a side elevational view of the probe of FIG. 3; and

FIG. 3B is a plan view of the probe of FIG. 3;

FIG. 4 is a waveform diagram of a normal maximum differential bubblepressure waveform showing three distinct hardware peak detector triggersignals: a valid peak at the maximum bubble pressure point (A); a falsepeak on a zero crossing (B); and a false peak on a capillary action (C);

FIG. 5 is a waveform diagram of a normal differential bubble pressurewaveform at thirty five bubbles per second showing the surface age anddead time;

FIG. 6 is a waveform diagram of a normal maximum differential bubblepressure waveform in water under 175 PSIG pressure showing the signaloscillating after each bubble is released;

FIG. 7 is an idealized pressure waveform showing the normal peak andfalling edge that occurs as each bubble forms and is released at anorifice;

FIG. 8 is an idealized pressure waveform showing a valid and false peakdue to a capillary action;

FIG. 9 is an idealized pressure waveform shooing the peak average of thesoftware peak detection algorithm and the tolerance window;

FIG. 10 is a dynamic surface tension plot for two different fluids;

FIG. 11 is a system block diagram showing the process for measuringsurface tension using the components of FIG. 1;

FIGS. 12 and 12A together comprise a system block diagram showing theprocess for measuring surface using the components shown in FIG. 2;

FIG. 13 is a simplified software flowchart showing the overall systemfor software peak detection;

FIGS. 14A and 14B together comprise a more detailed software flowdiagram of the advanced software peak detection routine of the presentinvention;

FIGS. 15A, 15B and 15C together comprise a software flow diagram of asoftware routine for detecting peak signals during bubbling;

FIG. 16 is a software flow diagram for detecting maximum and minimumvalues in a detection group;

FIG. 17 is a simplified block diagram representing the software routinefor sorting values; and

FIGS. 18A and 18B together comprise a software routine for calculatingthe results of the surface tension measurement.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings which illustrate a preferred embodiment of theinvention, and particularly to FIG. 1, an apparatus for determining thesurface tension of a liquid in a pressurized environment, up to but notlimited to 1000 psig (7000 kPa), includes a source of high pressurenitrogen or process gas (4) which is connected through appropriate highpressure tubing, fittings, or hoses to a pressure regulator means (5).

The invention includes means to accept a high input pressure source andreduce the pressure, as may be necessary to provide a correspondingprecise output mass flow control of the process gas, to the probeassembly, using one mass flow controller (mass flow controller) perorifice (6, 7), and where necessary, a third mass flow controller (8) asused in the two transducer (10, 11) scheme as illustrated in FIGS. 2 and12. The mass flow controllers used in one embodiment of the invention isa MKS Model 1261 rated for constant mass flow in the range from 0 to 100milliliters (SCCM) per minute.

The output of each mass flow controller (6, 7), illustrated in FIGS. 1and 11, is connected to a differential pressure transducer (10), ModelDP15 manufactured by Validyne Engineering Sales Corporation, through atee fitting (19); the negative (-ve) port of which is connected to thesmall orifice side and the positive (+ve) port of which is connected tothe large orifice side.

In the case of FIGS. 2 and 12, the two transducer, viscositycompensating configuration, each orifice is connected to the -ve portwith each +ve transducer port tied together and connected to the thirdmass flow controller (8), using a cross fitting (18) and then vented tothe pressure reactor atmosphere through an open vent fitting (17) or athird tube.

The outputs of the surface tension apparatus are connected topressurized tubing sections (20) that run to the reactor probe assembly,using high pressure tube fittings (21) welded to the top of the flange(22). The flange is designed for, and applicable to, the particularvessel, reactor, or process pipe. The small and large orifice probes aresimilarly connected and suspended from similar flange-welded tubefittings (21) on the underside of the flange and supported from lengthsof commercially available, fractional size, tubing (23), typically 0.25"or 6 mm. O.D. These tubes are housed within an elongated, perforated,protective rigid pipe or tube (24), threaded into a half coupling weldedto the underside of the flange, that allows varying the total length andtherefore the depth of penetration of the probes in the fluid by varyingthe length of the external pipe section and the internal connectingtubes, to suit the particular application. This arrangement is suitablefor top or bottom installation, and side installation with minormodifications.

A protective, ventilated or perforated, closed end "basket" arrangement(24), threaded onto the end of the protective pipe section through astandard pipe coupling (25), mitigates the effect of shearing orturbulence from the flow or mixing of the fluid in the vessel, reactor,or pipe, while at the same time allowing the free, non-turbulent flow ofthe fluid past the tension orifices and associated temperature (15), orother measurement probe. Additional internal tubing spacers (26) providerigidity to the system within the external pipe assembly and preventmovement of the probes within protective basket.

Standard tube fittings (27) allow replacement and interchange of probesand probe materials, including, but not limited to, glass, stainlesssteel, coated glass and steel, as well as straight or inverted probes.The tubing is pressure sealed, particularly for temperature and otherprocess measuring probes so as to prevent fluid ingress into the probesand associated electrical wiring. The entire assembly is modular innature for ease of assembly and disassembly for replacement and cleaningbetween process or production runs.

The temperature probe (15) is provided to sense temperature of theliquid under test since surface tension of a liquid is temperaturedependent in an inverse relationship. As temperature of the liquid goesup, surface tension decreases. An algorithm for surface tension versustemperature relationship for two standard calibration fluids is includedin the software, so that during the calibration sequence the computerprogram reads the temperature of the calibration fluid being used andautomatically inputs the correct surface tension value. Typical standardcalibration fluids are deionized water and ethyl alcohol. This algorithmcan also be used to temperature compensate surface tension values duringoperation.

The software program incorporates a sequential automatic flow controlsetting/calibration sequence that allows the automatic generation ofdynamic surface tension curves for tested fluids that contain activesurfactants (FIG. 10). The mass flow controllers are pre-programmed tosequence through a series of flow controller setting (i.e. 10, 20, 30,40, and 50 percent of full rating, for example) which result in fivedifferent and sequentially increasing bubble rates. First the probes areimmersed in a high standard calibration fluid (deionized water) and theprogram sequences through the different flow settings in a step-by-stepprocedure, pausing a sufficient period of time to allow analyzation ofthe differential pressure waveforms and the automatic input of thecorrect surface tension value for the high standard calibration fluid.This is repeated for the low standard calibration fluid (ethyl alcohol).Various test fluids are subsequently measured at these different flowrates and the resultant surface tension and bubble frequency data isplotted to give accurate dynamic surface tension curves (FIG. 10).

A power supply (9) provides operational power to the mass flowcontroller's. The mass flow controller input and output control signalsare routed, with analog input and output control signals from transducerdemodulator circuits (12), the temperature probe (15), and othersensors, to analog input and output interface boards (14) located in thecomputer (13) for processing by the software program. Since there is amaximum practical distance that the apparatus can be mounted away fromthe probe assembly and still retain signal sensitivity and desiredaccuracy, remote control of the apparatus and mass flow controllers isimportant in hazardous and explosive gas environments. A specificexample is application of the apparatus to monitor and control apolyvinyl chloride (PVC) polymerization reactor using combustible, vinylchloride gas in the reaction process. For this and similar applications,the apparatus is mounted in an explosion-proof housing, and/or in anitrogen purged enclosure, as may be required by local safety codesand/or standards.

The equipment arrangement in FIG. 2 allows correcting for viscosityeffects. An estimation of the hydrodynamic resistance of a fluid againsta moving bubble is done using Stokes law for a viscous resistance of aliquid. The correction value to calculated surface tension value, whichis the difference between measured value of dynamic surface tension andthe real value, is estimated by the following relationship ##EQU1##where: μ is the viscosity of the liquid,

γ is the surface tension of the liquid,

r is the radius of the orifice,

τ is the surface age.

Since the change in surface tension occurs at both the large and thesmall orifice, this relationship can be reduced to a simple relationshipof the radius of each of the orifice and the surface age of each bubblebeing formed. The bubble rate, and therefore the surface age, can beadjusted to cancel out the viscosity effect by setting the surface ageof each orifice in inverse relationship to the radii of the two orificesas follows: ##EQU2## where r₁ is the small orifice radius and r₂ is thelarge orifice radius.

An advanced software peak detection program was developed to mitigatethe problems encountered when using the hardware peak detection, and togive accurate surface tension measurements without false triggering ofthe peak detector in both ambient and pressurized environments. SeeFIGS. 11 and 12. This advanced software peak detection program has themeans to measure the maximum bubble pressure from a demodulator outputsignal that can be either unipolar or bipolar (both positive, orpositive and negative). It can measure fluids under pressure, withprovisions to reject false peaks caused by capillary action and otheroscillations. It can measure surface tension with provisions to rejectfalse peaks in very viscous fluids, and correct for viscosity effects,both in ambient and pressurized conditions.

Standard software peak detection techniques cannot distinguish betweenvalid peaks and peaks that are caused by noise (FIG. 8). Therefore, itwas necessary to develop this extension to the standard software peakdetection. The new advanced software peak detection algorithm uses theaverage of all valid peaks to compare each newly detected peak to it.Therefore, it has the ability to evaluate each newly detected peak asbeing valid or invalid. The user of the software has been given theflexibility to influence this detection by selecting the degree to whichdetected peaks are accepted as valid.

The system consists of two main parts, which are themselves divided intosub-systems (FIG. 13 through FIG. 18). The two main parts are: (1)Differential pressure signal analyzation, and (2) Differential pressuresignal peak detection.

Directly after the program starts, or when the probes are immersed intoa new sample, there is no average available to which the detected peakscan be compared to. Therefore, the signal has to be analyzed, meaningthe standard software peak detection is used to detect a certain numberof peaks. With these peak values the correct average can be determined,and is used from this point on in the advanced peak detection algorithm.

The differential pressure signal is represented in the computer byindividual integral numbers. See FIGS. 14A and 14B. Eight consecutivenumbers make up a detection group. See FIG. 16. Out of each detectiongroup, the maximum and minimum values are determined, also, theirindices in the memory buffer are stored. The maximum values are used todetect peaks in this algorithm in the following described procedure.

To detect a peak, the falling edge of the differential pressure signalhas to be detected first. A falling edge (FIG. 7) is defined by:

1. The difference between maximum and minimum value has to be higherthan 366 mV (+150 integral), to avoid detection of noise peaks.

2. The index of the minimum value has to be higher than the index of themaximum value, i.e. the minimum value has to appear after the maximumvalue in the same detection group.

The maximum value out of the current detection group is compared to themaximum value out of the preceding detection group. This is an importantstep, as well as a unique feature to this algorithm during peakdetection, as the peak can appear in a detection group I (FIG. 7) butthe falling edge is detected in detection group II. Using thiscondition, it is verified that a highly accurate peak value is deliveredby the peak detection algorithm.

During signal analyzation, the software tries to detect a certain numberof peaks. See FIGS. 15A and 15B. This number depends on the tolerancewindow settings. The relation between tolerance window setting andnumber of analyzation peaks is:

Tolerance window NARROW--10 peaks

Tolerance window MEDIUM--16 peaks

Tolerance window WIDE--20 peaks

After the necessary number of peaks are detected and stored, the peaksare sorted by value, in this case by using the bubble sort algorithm(FIG. 17). This algorithm is not restricted to one sorting method. Afterthe sort, the highest value in the analyzation array is in the top ofthe buffer, the lowest in the bottom.

                  EXAMPLE                                                         ______________________________________                                        Index          Before  After                                                  ______________________________________                                        0              1.85    -0.144                                                 1              4.38    0.591                                                  2              0.591   1.19                                                   3              4.31    1.26                                                   4              1.19    1.85                                                   5              4.32    4.31                                                   6              -0.144  4.32                                                   7              4.32    4.32                                                   8              1.26    4.38                                                   9              4.39    4.39                                                   ______________________________________                                    

After the values are sorted, out of the five highest values, (Index 5through 9) the correct peak average is calculated. Independently fromthe tolerance window setting, the five highest values are always usedfor the average calculation. This is derived from a differentialpressure signal that consists of valid peaks and peaks from capillaryactions (invalid peaks). This case can be considered the worst case, asthere are an even number of valid, high peaks, and invalid, low peaks.By considering only the upper part of the analyzation array, only thevalid peak values are used for the average calculation. This concludesthe analyzation.

During advanced peak detection, after a peak has been detected, therehas to be further examination of this value to evaluate if it is validunder the current circumstances. This evaluation makes this peakdetection algorithm advanced. See FIGS. 14A and 14B.

The detected peak value is compared to the current average of all theprevious valid peak values. For this comparison, a so-called tolerancewindow is applied. To compare the detected peak value to the currentpeak value average, the absolute value of the difference of peak valueand peak average must be lower than the tolerance value:

    ABS(peak.sub.13 value-peak.sub.13 average)<=tolerance.sub.-- value

If the result of this equation is True, the peak can be accepted asvalid. In this case, the new result for surface tension can becalculated.

The user adjustable tolerance window is a very unique feature of thissoftware. See FIGS. 8 and 9. With this window, two things are nowpossible:

1. Peaks that are caused by capillary actions can be rejected, so thatthey have no effect on the surface tension results.

2. It is possible to measure fluids of high viscosity, which havetypically inconsistent differential pressure signals.

Peaks caused by capillary action have typically a peak value that isabout 20% of that of peaks that appear when a bubble releases (FIG. 8).

With a standard peak detection algorithm, these two peaks cannot bedifferentiated, causing incorrect results for surface tension, as wellas for bubble frequency. With advanced peak detection, applying thetolerance window, peaks can be differentiated (FIG. 9). The tolerancewindow is a value range of ±tolerance around the peak average. The validpeak that is within the tolerance window can be accepted while thecapillary action is rejected.

To measure fluids with high viscosity even using the basic (FIG. 1)apparatus, the user can adjust this tolerance window to

Narrow (±300 mV)

Medium (±650 mV)

Wide (±1000 mV)

Since peak values of fluids typically fluctuate more than those of anon-viscous fluid, with the adjustable tolerance window the user candetermine which peaks are accepted, leading to a very accurate resultfor viscous fluids. Additionally, the averaging factor for the resultcalculation is increased with wider tolerance windows so that even withfluctuating peak values, a high stability of results can be expected.

Through a new averaging algorithm that is used in this software, twogoals are achieved: (1) higher stability of results compared to movingaverage; and (2) faster calculation of new average. See FIGS. 18A and18B.

For this averaging algorithm the averaging factor is introduced. Theaverage of a certain result (either surface tension, temperature orbubble frequency) is calculated by: ##EQU3##

The relation between tolerance window setting and number of analyzationpeaks is:

Tolerance window NARROW--averaging factor=10

Tolerance window MEDIUM--averaging factor=21

Tolerance window WIDE--averaging factor =33

This invention provides an apparatus for determining surface tension ofa liquid independent of the pressure environment of the containerholding the liquid or the depth of immersion of the probes under thesurface of the liquid.

This invention provides a software and hardware means to open the massflow controller control valve to its full open position to increase theflow through the mass flow controller to a maximum, in order to purgethe probes during the period that a vessel, reactor, or pipe ispressurized, so as to prevent the back flow of liquid into the probes,particularly fluids with high solids concentration that can causeplugging of the probes. This purging capability can also be used as ameans to unplug the probes during the normal production cycle, ifneeded, as can be appreciated from the incorporation of purging as theinitial step in both FIGS. 11-12.

While the form of apparatus herein described constitutes a preferredembodiment of this invention, it is to be understood that the inventionis not limited to this precise form of apparatus and that changes may bemade therein without departing from the scope of the invention, which isdefined in the appended claims.

What is claimed is:
 1. An apparatus for determining the surface tensionof a liquid comprisinga vessel, reactor, or process pipe system forcontaining a liquid under pressure; a pair of tubes having orifices ofdifferent diameters positioned below the surface of the liquid in saidvessel, reactor, or pipe system; means for adjusting the depth ofimmersion of the said orifices in the liquid; means for providing asource of gas pressure to said tubes using a separate mass flowcontroller for each tube; means connected between said source of gas andsaid tubes for providing a regulated, constant volume flow rate of gasto the tubes independently of pressure inside the vessel, reactor, orpipe system; means for automatically controlling the flow of gas to thetubes and therefore the bubble rate of gas at the orifices independentof the pressure inside said vessel, reactor, or pipe system; means formeasuring the maximum differential pressure of the bubbles forming atthe probes as a function of the surface tension of the liquid, using adifferential pressure transducer; means to measure the temperature of astandard calibration fluid and automatically calculate the correcttemperature compensated surface tension value; means to automaticallysequence the flow controller settings and generate dynamic surfacetension curves using a sequential flow-control setting/calibrationsequence.
 2. An apparatus for determining the surface tension of aliquid comprisingmeans to automatically control the bubble rate througha tube immersed in a vessel, reactor, or section of process pipe,independent of the pressure inside said vessel, reactor, or pipe, or thedepth of immersion; means to purge said tube during startup andoperation; means to measure the maximum bubble pressure signal from ademodulator output circuit that can be either unipolar or bipolar; meansto measure the maximum bubble pressure, and therefore the surfacetension of a liquid with provisions to reject false peaks caused bycapillary action independent of the pressure environment of the liquid;means to measure the maximum bubble pressure, and therefore the surfacetension of a liquid with provisions to reject false peaks caused byoscillations in the maximum bubble pressure waveform independent of thepressure environment of the liquid; means to measure surface tension ina viscous fluid with provisions to reject false peaks due tofluctuations of the differential pressure waveform caused by thehydrodynamic resistance of the viscous fluid against bubbles beingformed at the orifice; means to automatically measure the temperature ofa standard calibration fluid and choose the correct temperaturecompensated surface tension value; means to automatically sequence theflow controller settings and generate dynamic surface tension curvesusing a sequential flow-control setting/calibration sequence.
 3. Anapparatus for determining the surface tension of a liquidcomprisingmeans to automatically control the bubble rate through twotubes immersed in a vessel, reactor, or section of process pipeindependent of the pressure inside said vessel, reactor or pipe or depthof tube immersion; means to purge said tubes during startup andoperation; means to measure the maximum bubble pressure signals fromdemodulator output circuits that can be either unipolar or bipolar;means to measure the maximum bubble pressure and therefore the surfacetension of a liquid with provisions to reject false peaks caused bycapillary action independent of the pressure environment of the liquid;means to measure the maximum bubble pressure at an orifice and averagepeaks caused by oscillations in the maximum bubble pressure waveform ina pressurized environment and therefore determine the surface tension ofthe liquid; means to measure surface tension in a viscous fluid withprovisions to reject false peaks due to fluctuations of the differentialpressure waveform caused by the hydrodynamic resistance of the viscousfluid to a bubble being formed at the orifice; means to automaticallymeasure the temperature of a standard calibration fluid and calculatethe correct temperature compensated surface tension value; means toautomatically sequence the flow controller settings and generate dynamicsurface tension curves using a sequential flow-controlsetting/calibration sequence.
 4. An apparatus for determining thesurface tension of a liquid comprisingmeans to automatically control thebubble rate through two or more tubes with different orifice sizesimmersed in a vessel, reactor, or section of process pipe independent ofthe pressure inside said vessel, reactor or pipe or depth of immersionin the liquid; means to purge said tubes at any time during startup andoperation; means to measure the maximum bubble pressure signals fromdemodulator output circuits that can be either unipolar or bipolar;means to measure the maximum bubble pressure, and therefore the surfacetension of a liquid with provisions to reject false peaks caused bycapillary action independent of the pressure environment of the liquid;means to measure the maximum bubble pressures independently at twoorifices and reject false peaks caused by oscillations in the maximumbubble pressure waveforms in a pressurized environment, with means tosubtract the resulting maximum bubble pressure values to determine thedifferential and thereby determine the surface tension of the liquid;means to measure the maximum bubble pressure independently at each oftwo orifices in a viscous liquid and means to set the flow rates at eachorifice in a ratio that will cancel the effect of the hydrodynamicresistance of the viscous fluid to bubbles being formed at the orifices;means to automatically measure the temperature of a standard calibrationfluid and choose the correct temperature compensated surface tensionvalue; means to automatically sequence the flow controller settings andgenerate dynamic surface tension curves using a sequential flow-controlsetting/calibration sequence.
 5. In an apparatus for determining thesurface tension of a liquid includingat least two tubes (2,3) havingorifices of different diameters positioned below the surface of a liquidin a vessel, reactor, or section of process pipe; means for providing asource of gas (4) to said tubes; means connected between said source ofgas and tubes (6, 7) for providing a regulated, constant volume flowrate of gas to the tubes; means for controlling the flow of gas to theprobes (13) and therefore the bubble rate at the orifices; and means formeasuring the maximum differential pressure of the bubbles forming atthe probes as a function of the surface tension of the liquid, using adifferential pressure transducer (10); the improvement characterizedbymeans for adjusting the depth of immersion of the said orifices in theliquid (24); wherein said means for providing a source of gas pressureto said tubes includes a separate mass flow controller (6, 7) for eachtube; means to automatically measure the temperature (15) of a standardcalibration fluid and to calculate the correct temperature compensatedsurface tension value; and means to automatically sequence (13) the flowcontroller settings and generate dynamic surface tension curves using asequential flow-control setting/calibration sequence.
 6. The apparatusof claim 5 further comprisinga vessel, reactor, or process pipe systemfor containing a liquid under pressure; means connected between saidsource of gas and said tubes for providing a regulated, constant volumeflow rate of gas to the tubes independently of pressure inside thevessel, reactor, or pipe system; and means for automatically controllingthe flow of gas to the tubes and therefore the bubble rate of gas at theorifices independent of the pressure inside said vessel, reactor, orpipe system.
 7. An apparatus of claim 6 further comprisinga third massflow controller vented to the vessel atmosphere or to a third tube tooffset the pressure inside the vessel, reactor, or pipe system; meansfor measuring the maximum differential pressure of the bubbles formingat the probes as a function of the surface tension of the liquid, usingtwo or more differential pressure transducers with one common sideconnected to the pressurized system inside said vessel, reactor, or pipesystem.
 8. In an apparatus for determining the surface tension of aliquid comprisingat least two tubes having orifices of differentdiameters positioned below the surface of a liquid in a vessel, reactor,or section of process pipe; means for providing a source of gas to saidtubes; means connected between said source of gas and tubes forproviding a regulated, constant volume flow rate of gas to the tubes;means for controlling the flow of gas to the probes and therefore thebubble rate at the orifices; and means for measuring the maximumdifferential pressure of the bubbles forming at the probes as a functionof the surface tension of the liquid, using a differential pressuretransducer; the improvement characterized bymeans to automaticallycontrol the bubble rate through a tube immersed in a vessel, reactor, orsection of process pipe, independent of the pressure inside said vessel,reactor, or pipe, or the depth of immersion; means to purge said tubeduring startup and operation; means to measure the maximum bubblepressure signal form a demodulator output circuit that can be eitherunipolar or bipolar; means to measure the maximum bubble pressure andtherefore the surface tension of a liquid using automatic mass flowcontrollers that allow a predictable differential pressure signal to begenerated, means responsive to said differential pressure signal forrejecting false maximum bubble pressure signals due to fluctuations ofthe differential pressure waveform caused by the hydrodynamic resistanceof the viscous fluid against bubbles being form at the orifice; means toautomatically measure the temperature of a standard calibration fluidand choose the correct temperature compensated surface tension value;means to automatically sequence the flow controller settings andgenerate dynamic surface tension curves using a sequential flow-controlsetting/calibration sequence.
 9. The apparatus of claim 8 furthercomprisingmeans to measure the maximum bubble pressure, and thereforethe surface tension of a liquid with provisions to reject false peakscaused by capillary action independent of the pressure environment ofthe liquid; and means to measure the maximum bubble pressure at anorifice and to average the peaks caused by oscillations in maximumbubble pressure waveform in a pressurized environment and thereforedetermine the surface tension of the liquid.
 10. The apparatus of claim9 further comprisingmeans to measure the maximum bubble pressuresindependently at two orifices and reject false peaks caused byoscillations in the maximum bubble pressure wave forms in a pressurizedenvironment, with means to subtract the resulting maximum bubblepressure value to determine the differential and thereby determine thesurface tension of the liquid; means to measure the maximum bubblepressure independently at each of two orifices in a viscous liquid andmeans to set the flow rates at each orifice in a ratio that will cancelthe effect of the hydrodynamic resistance of the viscous fluid to bubblebeing formed at the orifices; and means to automatically measure thetemperature of a standard calibration fluid and choose the correcttemperature compensated surface tension value.